1. Field of the Invention
The present invention relates to a catalyst for producing phenol or alkyl phenol and to a method for producing phenol or alkyl phenol by gas phase oxidation of benzoic acid or alkyl benzoic acid under the presence of the catalyst.
2. Description of the Related Art
Various methods and catalysts are known to produce phenol by gas phase contact oxidation of benzoic acid.
For example, JP-A-57-11932 (the term JP-A- referred to hereinafter signifies unexamined Japanese patent publication) disclosed a catalyst containing at least one of a copper compound, a vanadium compound, a silver compound, a lithium compound, a sodium compound, and a magnesium compound, and a method using the catalyst.
JP-B-59-20384 (the term JP-B- referred to hereinafter signifies examined Japanese patent publication) disclosed a method using a catalyst containing oxides of copper, zirconium, and alkali metal and being supported on .alpha.-alumina. JP-B-64-934 disclosed a method using an oxide catalyst containing a variety of metallic elements: namely, molybdenum as the essential component, at least one of vanadium, niobium, and tantalum, and at least one of copper, silver, manganese, iron, cobalt, nickel, rhodium, palladium, and platinum, and at least one of thallium, an alkali metal, and an alkaline earth metal.
The inventors conducted extensive study on the catalyst for phenol production and on the method for producing phenol, and provided the catalysts to produce phenol by gas phase contact oxidation of benzoic acid, which catalysts include the catalyst of a nickel compound supported on a metallic oxide such as titania, magnesia, and .alpha.-alumina (JP-A-4-5250), the catalyst containing an iron oxide and a nickel oxide (JP-A-4-330944), the catalyst containing an iron oxide, a nickel oxide, and an alkali earth metal compound (JP-A-4-330945), the catalyst containing an iron oxide, a nickel oxide, and an alkali metal compound (JP-A-4-104837), the catalyst containing an iron oxide, a nickel oxide, an alkali metal compound, and an alkaline earth metal compound (JP-A-4-330946), and the catalyst containing a composite metallic oxide having a spinel crystal structure.
Furthermore, the inventors provided a catalyst to produce phenol by gas phase oxidation of toluene, which catalyst contains a vanadium oxide, an iron oxide, and a nickel oxide (JP-A-4-277029).
However, the catalyst disclosed in JP-A-57-11932 is insufficient in both activity and selectivity, and the method for producing phenol using the catalyst gives the conversion of benzoic acid of 50.5% and the selectivity to phenol of 88.6% at the maximum. In addition, when an exothermic reaction such as oxidation of benzoic acid is carried out using a catalyst containing a copper compound, the catalyst bed likely induces hot spots which raises a problem of sintering of the catalyst and of significant degradation of the activity. The method for producing phenol disclosed in JP-B-59-20384 also shows an insufficient conversion and selectivity giving the conversion of benzoic acid of 63.7% and the selectivity to phenol of 82.2% at the maximum. Furthermore, the method induces the yield of a large amount of by-products such as diphenyl oxide, which significantly degrades the catalyst activity. The method also has an industrial disadvantage of necessity of refining stage for produced phenol.
The method for producing phenol disclosed in JP-B-64-934 also gives the conversion of benzoic acid of 75% and the selectivity to phenol of 89% at the maximum, which values are insufficient for industrial application. The method also has a problem of catalyst degradation with time.
All the three of above described methods gives a low space time yield of phenol (production amount of phenol per unit catalyst volume per unit time) not higher than 100, so the productivity is poor, and the methods are inapplicable to industrial process.
Regarding the production of cresol from toluic acid, which was disclosed in JP-B-64-934, the catalyst activity and the selectivity are insufficient giving the conversion of 45% and selectivity to m-cresol of 81% for the reaction of p-toluic acid (4-methyl benzoic acid), and gives the conversion of 48% and the selectivity to m-cresol of 79% for the reaction of o-toluic acid (2-methyl benzoic acid). M. Hronec, et al. pointed out a difficulty for obtaining a high yield of cresol species in the reaction system using a catalyst containing Cu owing to the unstable intermediate reaction products (Applied Catalysis, 69 (1991) pp201-204). In addition, the method has the problem of significant degradation of catalyst activity and of low space time yield, which is similar to the problem in the case of synthesis of phenol from benzoic acid.
The catalysts which were presented by the inventors improved the above described problems and improved the conversion of benzoic acid and the selectivity to phenol. Nevertheless, the development of catalysts which further improve the catalyst life and which are applicable to other reaction systems such as the ones to obtain alkyl phenol such as cresol from alkyl benzoic acid at a high yield have been wanted.